A disk image is a snapshot of a storage device's content typically stored in a file on another storage device. Compression and deduplication are commonly used to further reduce the size of image files.
Disk imaging is performed for a variety of purposes including digital forensics, cloud computing, system administration, backup,
Despite the benefits, storage costs can be high, ISO images are intended to emulate optical media, such as a CD-ROM. Raw disk images are used for forensic purposes. Disk images became much more popular when floppy disk media became popular, where replication or storage of an exact structure was necessary and efficient, especially in the case of copy protected floppy disks.
Disk image creation is called disk imaging and is often time consuming, even with a fast computer, because the entire disk must be copied. In Unix or similar systems the dd program can be used to create raw disk images. A virtual burner, by definition, appears as a disc drive in the system with writing capabilities (as opposed to conventional disc authoring programs that can create virtual disk images), thus allowing software that can burn discs to create virtual discs.
Uses
Digital forensics
Forensic imaging is the process of creating a bit-by-bit copy of the data on the drive, including files, metadata, volume information, filesystems and their structure. Further, there are less issues with wear and tear. A hard disk drive or solid-state drive in a virtual machine is implemented as a disk image (i.e. either the VHD format used by Microsoft's Hyper-V, the VDI format used by Oracle Corporation's VirtualBox, the VMDK format used for VMware virtual machines, or the QCOW format used by QEMU). Virtual hard disk images tend to be stored as either a collection of files (where each one is typically 2GB in size), or as a single file. Virtual machines treat the image set as a physical drive.
Rapid deployment of systems
Educational institutions and businesses can often need to buy or replace computer systems in large numbers. Disk imaging is commonly used to rapidly deploy the same configuration across workstations. This image is then written to a computer's hard disk (which is sometimes described as restoring an image).
Network-based image deployment
Image restoration can be done using network-based image deployment. This method uses a PXE server to boot an operating system over a computer network that contains the necessary components to image or restore storage media in a computer. This is usually used in conjunction with a DHCP server to automate the configuration of network parameters including IP addresses. Multicasting, broadcasting or unicasting tend to be used to restore an image to many computers simultaneously.
Digital preservation
Libraries and museums are typically required to archive and digitally preserve information without altering it in any manner. Emulators frequently use disk images to emulate floppy disks that have been preserved. This is usually simpler to program than accessing a real floppy drive (particularly if the disks are in a format not supported by the host operating system), and allows a large library of software to be managed. Emulation also allows existing disk images to be put into a usable form even though the data contained in the image is no longer readable without emulation. When imaging multiple computers with only minor differences, much data is duplicated unnecessarily, wasting space.